This application is related to application Ser. No. 09/932,482, entitled xe2x80x9cSingle-Blade Underreamer,xe2x80x9d filed on Aug. 17, 2001.
This invention relates in general to the field of subterranean exploration and, more particularly, to a multi-blade underreamer.
Underreamers are generally used to form an enlarged cavity in a well bore extending through a subterranean formation. The cavity may then be used to collect resources for transport to the surface, as a sump for the collection of well bore formation cuttings and the like, or for other suitable subterranean exploration and resource production operations. Additionally, the cavity may be used in well bore drilling operations to provide an enlarged target for constructing multiple intersecting well bores.
One example of an underreamer includes a plurality of cutting blades pivotally coupled to a lower end of a drill pipe. Centrifugal forces caused by rotation of the drill pipe extends the cutting blades outwardly and diametrically opposed to each other. As the cutting blades extend outwardly, the centrifugal forces cause the cutting blades to contact the surrounding formation and cut through the formation. The drill pipe may be rotated until the cutting blades are disposed in a position substantially perpendicular to the drill pipe, at which time the drill pipe may be raised and/or lowered within the formation to form a cylindrical cavity within the formation.
Conventional underreamers, however, suffer several disadvantages. For example, the underreamer described above generally requires high rotational speeds to produce an adequate level of centrifugal force to cause the cutting blades to cut into the formation. An equipment failure occurring during high speed rotation of the above-described underreamer may cause serious harm to operators of the underreamer as well as damage and/or destruction of additional drilling equipment.
Additionally, density variations in the subsurface formation may cause each of the cutting blades to extend outwardly at different rates and/or different positions relative to the drill pipe. The varied positions of the cutting blades relative to the drill pipe may cause an out-of-balance condition of the underreamer, thereby creating undesired vibration and rotational characteristics during cavity formation, as well as an increased likelihood of equipment failure.
Accordingly, a need has arisen for an improved underreamer that provides increased control of subterranean cavity formation. The present invention provides a multi-blade underreamer that addresses shortcomings of prior underreamers.
According to one embodiment of the present invention, a multi-blade underreamer for forming a cavity within a well bore includes a housing rotatably disposed within the well bore. The underreamer also includes a plurality of cutting blades pivotally coupled to the housing. The underreamer also includes a piston slidably disposed within the housing and adapted to engage the cutting blades. The piston is operable to receive a downwardly disposed force operable slide the piston relative to the housing such that the sliding of the piston causes extension of the cutting blades outwardly from a retracted position relative to the housing. The underreamer further includes a passage disposed within the piston and operable to communicate a fluid received via an annulus of the housing to the cutting blades.
According to another embodiment of the present invention, a method for forming a cavity within a well bore includes providing an underreamer within a well bore. The underreamer includes a plurality of cutting blades pivotally coupled to a housing for forming the cavity. The method also includes directing a fluid downwardly within an annulus of the housing, and receiving the fluid at a piston of the underreamer. The piston is slidably disposed within the housing and coupled to the cutting blades such that the fluid is operable to move the piston relative to the housing. The method further includes rotating the underreamer within the well bore and extending the cutting blades outwardly from a retracted position relative to the housing in response to the movement of the piston relative to the housing. The method further includes directing the fluid outwardly from the annulus to the cutting blades.
The invention provides several technical advantages. For example, according to one embodiment of the present invention, a downwardly directed force is applied to a piston of the underreamer to cause outwardly directed movement of a plurality of cutting blades into a subterranean formation. The downwardly directed force applied to the piston may be varied to produce corresponding varying pressures on the formation by the cutting blades. Thus, the present invention may be used to accommodate a variety of formation densities and compositions. Additionally, decreased rotational speeds of the underreamer may be used to form the cavity, thereby substantially reducing or eliminating hazards associated with high speed rotating mechanisms.
Another technical advantage of the present invention includes regulating the pressure applied to the subsurface formation via the cutting blades using a fluid while directing a portion of the fluid to the cutting blades to enhance cutting removal and well bore cleaning. For example, according to one embodiment of the present invention, a pressurized fluid is applied downwardly to a piston to cause outwardly radial movement of the cutting blades into the subsurface formation. The piston includes a passage to communicate a portion of the fluid to the cutting blades via circulation ports disposed in a housing of the underreamer. Thus, the pressure applied to the formation may be varied to accommodate a variety of formation densities while providing fluid to the cutting blades to accommodate cutting removal and well bore cleaning.